When we speak of construction, we mean the material used in building
and the way it is put together. The different historical periods of
building are now classed into distinct dates, which have been arrived
at by observing the material used, and the way it is used, in
buildings of which there is no doubt as to the date of erection, and
comparing it with others. The early Greek Period in Italy is marked by
massive walls of masonry--walls built from the stone of the vicinity,
the blocks being rough as hewn out of the quarry,--polygonal. The
later Greek Period and the Etruscan are identical, being formed of
square blocks of stone, headers, and stretchers. In the time of the
kings of Rome the stones were squared, and were of tufa, lapis ruber,
tophus. In the earliest walls they are close jointed; in the second
period the edges are bevelled.
During the Republic the stones were also squared, but the material was
of peperino. Lapis Albanus and other forms of working up the material
were introduced. Pieces of stone, fixed together with cement, gave a
new kind of wall called _opus incertum_. This was improved upon by
facing the outside of the small pieces of stone and making them of one
uniform size--small polygonal. Then the stones were cut into wedge
shapes: the point being inwards, and being laid in regular rows it has
the appearance of network, and is called _opus reticulatum_. This
work, introduced in the last years of the Republic, went out of
fashion after the time of Tiberius, but was revived by Hadrian, who
always set his reticulated work in bands of brick like a picture
frame, thus distinguishing his from the earlier work, the inside of
the walls in those cases being concrete. The earliest brick building
which we have is the Pantheon. Thus it was under Augustus that brick
was first used by the Romans. It was his boast that he found Rome of
brick, and left it marble; which is only true in a certain sense, for
he did not build of solid marble, but cased veneering marble on to the
brickwork.
One period of Roman brickwork can easily be distinguished from the
others by measuring the number of bricks in a foot, and noticing their
uniformity of size. This, of course, does not refer to ornamental
brickwork. The brickwork of Nero is the best in the world--thin narrow
bricks, tiles, with very little mortar between them. Before his time
it was not quite so good; but after, it gradually declined till the
cement is as thick as the bricks.
The stone used during the Empire was travertine, _lapis Tiburtinus_,
but brick was the material generally used then. They are of two
colours, red and yellow, according to the clay from which they were
made. The walls were not of solid brick all through; but the interior
was made of pieces--rubble-work--the outside course being entire
brick, whilst at every four or five feet all through the construction
were laid the great tie-bricks to keep the rubble-work from shifting.
The brickwork was called _opus lateritium_. The great tie-bricks are
usually stamped with the names of the consul or emperor and the maker,
and these date the walls by measuring the number of bricks there are
in a foot. In the fourth century another system--_opera
decadence_--came into vogue, and walls were built with layers of brick
and pieces of tufa-stone a little larger than our English bricks. This
work continued down to the thirteenth century, when _opera
Saracenesca_--tufa-stones without the bricks between--came into use.
In the stone walls no cement was used; one stone was simply placed
upon another, its weight keeping it in its place, and clamps were
inserted to keep it from shifting. In the walls of Roma Quadrata we
know of no clamps having been found; but in the wall of the two kings
wooden clamps were found. In the walls of Servius Tullius iron clamps
were found; and in the Colosseum clamps can still be seen in several
places where pieces of the facing of the stone have been split off.
Tufa is found all over the Campagna, and is of volcanic origin. When
the Alban Hills were active volcanoes, the ashes and scoriæ thrown up
fell into the sea, now the Campagna. The pressure of water on it
formed it into stone: where there has been a great pressure, it is
very hard; where little pressure, it is softer; and where there was no
pressure, it still remains a sort of sand--this mixed with live lime
is the celebrated Roman cement. The softer tufa was used by the Greek
colonists, and the hard stone by the kings of Rome. Some tufa from the
neighbourhood of Gabii is dark gray, the other is brown and reddish.
Peperino is also volcanic. It was ejected in the shape of hot mud from
the volcano, and on cooling formed a good stone: this comes from the
Alban hills, and was used in the time of the Republic.
Travertine comes from Tivoli, and is a petrifaction formed by the
action of lime and sulphur on vegetable decay. This was not used as a
building material to any great extent before the time of Cæsar. It is
white, and becomes yellow on exposure. Silex is another volcanic stone
very little used for building, but entirely for paving the roads both
ancient and modern. This came out of the volcano as a red-hot stream
of lava, and on cooling down became a capital paving material. The bed
of the road was first properly prepared, and then it was paved with
polygonal blocks of blue basalt called silex. The stones fitted close
to one another. Many of the roads are in a good condition to this day;
the best specimen is opposite the Temple of Saturn in the Forum, B.C.
175. This stone is used for _opus reticulatum_ in some of the tombs on
the Appian Way and at the Temple of Hercules; also for concrete.